Calcium phosphate salts provide the hardness and rigidity which uniquely characterize normal, healthy bones and teeth. Developmental defects in the deposition of these salts or their destruction and loss by disease can severely impair the function of these skeletal tissues. The purpose of this project is to study the physical, chemical, and ultrastructural properties of these salts, and to clarify the kinetic and thermodynamic processes and the interactions with substances of biological interest that uniquely enable these salts to carry out their specialized role in vivo. The properties of calcium phosphate salts are being studied with a variety of ultrastructural and physical-chemical techniques such as electron microscopy, x-ray diffraction, surface area analyses, chromatographic and standard analytical chemistry procedures. Topics under current investigation include the formation and properties of precipitates induced in phosphate solutions by the ionophoric translocation of calcium ions across lipophilic solvent barriers, and (2) the modulation by enamel proteins of crystal growth processes in supersaturated solutions seeded with apatite. The ionophore experiments are being conducted with liposomes with the goal of better understanding how matrix vesicles, the loci for initial mineralization in many vertebrate hard tissues, can concentrate to precipitable levels calcium and phosphate in their membrane and interior spaces. The purpose of the protein-modulated crystal growth experiments is to better elucidate the role enamel matrix proteins play in enamel apatite nucleation and growth.